There is an increasing demand from e.g. train passengers to be able to communicate through mobile phones and other hand-held terminals while traveling, and also to access the Internet with laptop computers etc. However, train carriages are made of metal, and even the windows are normally covered with a metal film. Accordingly, train carriages are shielded compartments, and direct communication between terminal antennas within the carriages and externally located antennas is difficult to obtain. Further, with continuously operating software applications on ubiquitous hand-held devices, large numbers of cellular network hand-overs are required when the train moves. Even though this problem is common for all moving vehicles, it is especially pronounced for vehicles moving at high speed with many passengers, such as trains. This puts a strain on the wireless network infrastructure, leading to poor performance.
The mobile nature of a client with respect to the base stations may also introduce several potential sources of communication performance degradation. Such sources may derive from complex terrain, competition for available channels, or the source may be an unknown source of noise related to e.g. radio-frequency interference.
To this end, train carriages are often provided with an external antenna connected to a repeater unit within the carriage, which in turn is connected to an internal antenna. Hence, the communication between the passengers' terminals and the operator antennas outside the trains occurs through the repeater unit. Similarly, it is known to provide a mobile access router for data communication, also connected both to an external antenna and an internal antenna, in each carriage, in order to provide Internet access on board the train. Such mobile access router solutions are e.g. commercially available from the applicant of the present application, Icomera AB, of Gothenburg, Sweden, and are also disclosed in EP 1 175 757 by the same applicant. This method, hereinafter referred to as “aggregation”, has greatly improved the reliability of high-bandwidth wireless communication for trains and other large vehicles. However, this solution may still be insufficient to obtain an optimal transmission performance, especially for large data volumes. Trains and other moving vehicles often pass through areas with bad radio coverage, and present solutions are often unable to handle the required traffic.
Further, e.g. the current rising trend of streaming media uses far more data per minute of journey per passenger than older uses of the Internet, such as browsing text- and image-based sites like Facebook, or checking and responding to email.
Routing all traffic from a vehicle to a gateway, an aggregation server, also puts a strain on the gateway. The performance of that gateway is a natural bottleneck in the system when the data volume increases. Each train may have more than one router, and even if each router may have its own gateway, if multiple gateways are co-located at the same physical site, the wired network infrastructure of that site is still a potential limiting factor. With the continuing popularization, utilization and improvement of wireless Internet communication, it will soon be economically infeasible to maintain numerous stationary gateways with terabit bandwidth or more to serve large fleets of vehicles using LTE-A or similar, more sophisticated technologies.
There is therefore a need for an improved method and system for communicating with clients on moving vehicles, and in particular trains, allowing increased capacity, capacity utilization, quality and/or cost-efficiency. Even though the above discussion is focused on trains, similar situations and problems are encountered in many other types of moving vehicles, and in particular moving passenger vehicles, such as buses, ships and airplanes.